Gettering using voids formed by surface transformation

ABSTRACT

One aspect of this disclosure relates to a memory device, comprising at least one gettering region, a memory array, a plurality of word lines and bit lines, and control circuitry. The gettering region is formed in a semiconductor substrate. The gettering region includes a precise arrangement of precisely-formed voids to getter impurities from a crystalline semiconductor region of the substrate. The memory array is formed in the crystalline semiconductor region, and includes a plurality of memory cells formed in rows and columns, and at least one transistor for each of the plurality of memory cells. Each word line is connected to a row of memory cells, and each bit line is connected to a column of memory cells. The control circuitry includes word line select circuitry and bit line select circuitry to select a number of memory cells for writing and reading operations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 37 C.F.R. 1.153(b) of U.S.application Ser. No. 10/931,344, filed Aug. 31, 2004, which is adivisional of U.S. application Ser. No. 10/623,794, filed on Jul. 21,2003, now issued as U.S. Pat. No. 6,929,984, both of which areincorporated herein by reference in their entirety.

This application is related to the following commonly assigned U.S.patent applications which are herein incorporated by reference in theirentirety: “Cellular Materials Formed Using Surface Transformation,”application Ser. No. 10/382,246, filed Mar. 5, 2003; “Gettering ofSilicon On Insulator Using Relaxed Silicon Germanium Epitaxial ProximityLayers,” application Ser. No. 10/443,337, filed May 21, 2003; and “WaferGettering Using Relaxed Silicon Germanium Epitaxial Proximity Layers,”application Ser. No. 10/443,339, filed May 21, 2003.

TECHNICAL FIELD

This disclosure relates generally to integrated circuits, and moreparticularly, to strained semiconductor structures.

BACKGROUND

Unwanted crystalline defects and impurities can be introduced duringcrystal growth or subsequent wafer fabrication processes. These defectand impurities can degrade device characteristics and overall yield.Gettering has been described as a process for moving contaminants and/ordefects in a semiconductor into its bulk and away from its top surfaceto create a denuded zone cleared from contaminants and/or defects.Preferably, devices are built in the denuded zone.

Historically, extrinsic backside gettering was used to getter siliconwafers. Various extrinsic backside gettering processes involve damagingthe backside of the wafer mechanically or by implanting argon,germanium, hydrogen or other implants, or providing a gettering layer onthe backside of the wafer using a phophorosilicate glass or oxidebackside layer, a polysilicon backside layer, and a silicon germanium(SiGe) backside epitaxial layer. Subsequently, “intrinsic” gettering wasdeveloped, which employed oxygen precipitation and “bulk microdefects”precipitated into the bulk of the wafer after the surface was “denuded”of oxygen. The precipitation process, the gettering effects, and theelectrical characterization of defects and gettering silicon wafers havebeen investigated. Recently, intrinsic gettering modifications have beendeveloped, including neutron irradiation, high boron doping, nitrogendoping, and the use of magnetic fields during crystal growth.

These gettering processes depend on the diffusion of unwanted impuritiesover significant distances from desired device regions to the getteringsites. However, modern low temperature processes have small thermalbudgets, and do not afford an opportunity for significant diffusion ofdopants and/or unwanted impurities. Thus, it is desirable to reduce thedistance between the gettering sites and the device area. It has beenpreviously proposed to implant various impurities in proximity to thedevice areas, to co-implant oxygen and silicon to form a gettering layerin close proximity to the device area, to implant helium to formcavities close to the device areas which getter impurities, and togetter material in trench isolation areas in close proximity to thedevice areas.

Implanting helium forms cavities that function to getter impurities.This helium implantation technique has been proposed to getter both bulkand silicon-on-insulator devices. However, the location and density ofthese cavities formed by implanting helium is random. One problemassociated with the random location and density of cavities is that theeffectiveness of the gettering unwanted impurities from the desireddevice regions is inconsistent. Other problems associated with therandom location and density of cavities involves the varying strain inthe substrate and the varying ability of the substrate to withstandmechanical strain. The inconsistent effectiveness of gettering, theinconsistent strain and the inconsistent ability to withstand strain cannegatively affect the ability to precisely form devices as thesemiconductor industry strives to fabricate smaller and thinner devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a semiconductor structure having a gettering regionwith precisely formed voids at precise locations, according to variousembodiments of the present invention.

FIG. 2 illustrates a semiconductor structure having a gettering regionwith precisely formed voids at precise locations, according to variousembodiments of the present invention.

FIG. 3 illustrates a transistor formed in a device region proximate to agettering region with precisely formed voids at precise locations,according to various embodiments of the present invention.

FIGS. 4A-4F illustrate a process to form a sphere-shaped empty space ina gettering region, according to various embodiments of the presentinvention.

FIGS. 5A-5C illustrate a process to form a pipe-shaped empty space in agettering region, according to various embodiments of the presentinvention.

FIGS. 6A-6B illustrate a process to form a plate-shaped empty space in agettering region, according to various embodiments of the presentinvention.

FIGS. 7A-7E illustrate the formation of empty spheres in a getteringregion from initial cylindrical holes with the same radii and withvarying length, according to various embodiments of the presentinvention.

FIG. 8 illustrates a transformation formed stack of empty plates in agettering region, according to various embodiments of the presentinvention.

FIG. 9 illustrates fourteen representative unit cells of space latticeswhich the voids in the gettering region can form, according to variousembodiments of the present invention.

FIG. 10 illustrates a void pattern in a gettering region arranged toform the cubic P unit cell shown among the fourteen representative unitcells of FIG. 9.

FIGS. 11A-11B illustrate a process for forming a cubic P lattice ofspherical empty spaces, according to various embodiments of the presentinvention.

FIGS. 12A-12D illustrate a process for forming a simple unit of emptyspheres having two radii in a gettering region, according to variousembodiments of the present invention.

FIG. 13 illustrates a process for forming semiconductor devices,according to various embodiments of the present invention.

FIG. 14 illustrates a process for precisely forming voids in a substratelocated to getter a device region as performed in the process forforming semiconductor devices of FIG. 13.

FIG. 15 is a simplified block diagram of a high-level organization of amemory device, according to various embodiments of the presentinvention.

FIG. 16 is a simplified block diagram of a high-level organization of anelectronic system, according to various embodiments of the presentinvention.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingswhich show, by way of illustration, specific aspects and embodiments inwhich the present invention may be practiced. The various embodimentsare not necessarily mutually exclusive as aspects of one embodiment canbe combined with aspects of another embodiment. Other embodiments may beutilized and structural, logical, and electrical changes may be madewithout departing from the scope of the present invention. In thefollowing description, the terms wafer and substrate are interchangeablyused to refer generally to any structure on which integrated circuitsare formed, and also to such structures during various stages ofintegrated circuit fabrication. Both terms include doped and undopedsemiconductors, epitaxial layers of a semiconductor on a supportingsemiconductor or insulating material, combinations of such layers, aswell as other such structures that are known in the art. The terms“horizontal” and “vertical”, as well as prepositions such as “on”,“over” and “under” are used in relation to the conventional plane orsurface of a wafer or substrate, regardless of the orientation of thewafer or substrate. References to “an”, “one”, or “various” embodimentsin this disclosure are not necessarily to the same embodiment, and suchreferences contemplate more than one embodiment. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims,along with the full scope of equivalents to which such claims areentitled.

Various aspects and embodiments of the present invention getter asemiconductor wafer by precisely forming voids, such as nano-sizedvoids, at desired locations in the wafers. Thus, precisely-formedgettering void patterns are formed in selected regions below wheredevices are fabricated on semiconductor wafers. Numerous dangling bondsare present at the internal surfaces of the voids such that theseinternal surfaces are highly chemically reactive. Thus, variousembodiments form the voids and void patterns to have a large surface tovolume ratio to increase gettering of impurities.

One aspect of this disclosure relates to a method for creating agettering site in a semiconductor wafer. In various embodiments, apredetermined arrangement of a plurality of holes is formed in thesemiconductor wafer through a surface of the wafer. The wafer isannealed such that the wafer undergoes a surface transformation totransform the arrangement of the plurality of holes into a predeterminedarrangement of at least one empty space of a predetermined size withinthe wafer to form the gettering site.

One aspect relates to a semiconductor wafer. In various embodiments, thewafer includes at least one device region, and at least one getteringregion located proximate to the at least one device region. Thegettering region includes a precisely-determined arrangement of aplurality of precisely-formed voids that are formed within the waferusing a surface transformation process. Other aspects and embodimentsare provided herein.

Aspects of the present invention precisely form voids at desiredlocation using a surface transformation process to getter semiconductorwafers. Various embodiments precisely form patterns of nano-voids (voidshaving a diameter on the order of a nanometer) as a proximity getteringregion to effectively and consistently getter impurities from deviceregions.

FIG. 1 illustrates a semiconductor structure having a gettering regionwith precisely formed voids at precise locations, according to variousembodiments of the present invention. The illustrated structure 100includes a semiconductor wafer, also referred to here as a substrate101. A proximity gettering region 102 is located near to a device region103 such that unwanted impurities can travel a short distance from thedevice region 103 to the gettering region 102, even with modern lowtemperature processes. The gettering region 102 includes a number ofprecisely formed and located voids 104 formed by surface transformation.Surface transformation is described in detail below. The presentinvention is not limited to gettering regions having a particularpattern, shape or size of voids. In various embodiments, the deviceregion 103 includes crystalline silicon. Semiconductor devices, such astransistors, are fabricated in the crystalline silicon. Othercrystalline semiconductor materials can be used to form the deviceregion 103. Thus, it is desired to getter unwanted impurities from thedevice region. The voids 104 in the gettering region 102 generatedefects that getter impurities from the device region 103. The internalsurfaces of the voids have numerous dangling bonds, and thus are highlychemically reactive, which serves to getter impurities from the deviceregion 103.

FIG. 2 illustrates a semiconductor structure having a gettering regionwith precisely formed voids at precise locations, according to variousembodiments of the present invention. The illustrated structure 200includes a semiconductor wafer, also referred to here as a substrate201. A number of proximity gettering regions 202 are located near to anumber of device regions 203 such that unwanted impurities can travel ashort distance from the device regions 203 to the gettering regions 202,even with modern low temperature processes. The gettering region 202includes a number of precisely formed and located voids 204. The presentinvention is not limited to gettering regions having the illustratedpattern, size or shape of voids. The voids create defects that arehighly chemically reactive and serve to getter impurities from thedevice region 203.

FIG. 3 illustrates a transistor formed in a device region proximate to agettering region with precisely formed voids at precise locations,according to various embodiments of the present invention. Theillustrated transistor 305 is fabricated over a proximity getteringregion 302. The gettering region 302 has a predetermined and precisearrangement of precisely formed voids 304. A gate oxide 306 is formed onthe substrate 301, and a gate is formed over the gate oxide. First andsecond diffusion regions 308 and 309 are formed. A transistor channelregion 310 is formed between the first and second diffusion regions 308and 309. Other devices, such as capacitors and diodes, can be formed indevice regions proximate to a gettering region. These gettering regionsand device regions can be formed in both bulk andsemiconductor-on-insulator (SOI) technology. Furthermore, thesegettering regions can be used to getter both strained and unstraineddevice regions.

In various embodiments, the precisely-determined arrangement of voidsprovides the gettering region with voids that are more uniformly spacedand with a majority of voids that are closed voids. The uniformity,density, and space symmetry of the voids in the gettering region isprecisely determined by controlling the diameter, depth and position ofan initial arrangement of cylindrical holes formed through a surface ofa solid (e.g. a surface of a semiconductor wafer). In variousembodiments, the holes have a generally-elongated shape extending intothe volume away from the surface. In various embodiments, the holes havea generally cylindrical shape. The present subject matter is not solimited, however.

The voids in the gettering region generate defects that getterimpurities from the device region. The internal surfaces of the voidshave numerous dangling bonds, and thus are highly chemically reactivewhich serves to getter impurities from the device region. Thus, variousembodiments for voids and voids patterns to have a large surface tovolume ratio to increase the gettering of impurities. In variousembodiments, the precisely-determined arrangement of voids provides thesemiconductor wafer with a predictable mechanical failure for a givenforce. In various embodiments, the precisely-determined arrangement ofvoids provides the semiconductor wafer with an anisotropic stiffness.

When a solid is heated to a higher temperature, a solid with a hole thatis beyond a critical length (λ_(c)) becomes unstable. For the purposesof the analysis provided below, the holes are referred to as cylindricalholes. Upon reading and comprehending this disclosure, one of ordinaryskill in the art will understand that holes which are not geometricallycylindrical can be used in a surface transformation process, and furtherwill understand how to form a predetermined arrangement of voids usingholes that are not geometrically cylindrical.

The cylindrical hole is transformed into one or more empty spheresformed along the cylinder axis. The number (N) of spheres formed dependson the length (L) and radius (R_(C)) of the cylinder. Two models ofdiffusion are the surface diffusion model and the pure volume diffusionmodel. With respect to the surface diffusion model, for example, therelation between the cylinder length (L), cylinder radius (R_(C)), andnumber of spheres (N) is expressed by the following equation:8.89×R _(C) ×N≦L<8.89×R _(C)×(N+1).  (1)Equation (1) predicts that no empty spheres will form if L<8.89×R_(C).Each empty sphere that forms has a radius (R_(S)) expressed by thefollowing equation:R _(S)=1.88×R _(C).  (2)If the cylinder has sufficient length L to form two spheres, thecenter-to-center spacing between the spheres corresponds to the criticallength (λ_(C)) and is provided by the equation:λ_(C)=8.89×R _(C).  (3)The pure volume diffusion model provides similar results, with slightlydifferent constants. For example, depending on the exact magnitude ofthe diffusion parameters, λ_(C) can vary from 9.02×R_(C) to 12.96×R_(C).One of ordinary skill in the art will understand, upon reading andunderstanding this disclosure, that the diffusion model is capable ofbeing determined by experiment. The remainder of this disclosure usesthe surface diffusion model. One of ordinary skill in the art willunderstand, upon reading and comprehending this disclosure, how to applythis disclosure to another diffusion model.

Various shaped empty spaces or voids such as sphere-shaped voids,pipe-shaped voids, and plate-shaped voids are capable of being formedunder the surface of a semiconductor substrate or wafer with awell-defined melting temperature. The shape of the empty spaces formedduring the annealing conditions depends on the size, number and spacingof the cylindrical holes that are initially formed at a lowertemperature.

Various predetermined arrangements of empty spaces or voids are capableof being formed under the surface of a semiconductor substrate or waferwith a well-defined melting temperature. For example, anappropriately-sized deep trench in a material with a well-definedmelting temperature is transformed into empty spheres along the axis ofthe original trench at an annealing temperature within a predetermined arange below the melting temperature. The empty spheres are uniformlysized and spaced. Other predetermined arrangements are provided below.

FIGS. 4A-4F illustrate a process to form a sphere-shaped empty space ina gettering region, according to various embodiments of the presentinvention. A cylindrical hole 411 is formed through the surface 412 of asemiconductor volume where at least part of the volume forms a getteringregion 402. As used here, the term hole refers to a void that extendsfrom a surface of the volume into the solid material and that is definedby the solid material. The semiconductor volume 402 is heated (annealed)and undergoes the transformation illustrated in FIGS. 4B through 4F. Oneof ordinary skill in the art would understand, upon reading andcomprehending this disclosure, that the desired annealing temperature isdependent on the well-defined melting temperature of the semiconductormaterial. The result of the surface transformation process is an emptysphere 413 formed below the surface 412 of the semiconductor volume 402.

In order to form a single sphere, which holds true for forming a singlepipe (FIGS. 5A-5C) or plate (FIGS. 6A-6B), the length (L) and radius(R_(C)) of the cylindrical holes are chosen such that equation (1) withN=1 is satisfied. A vertical stacking of N empty spaces results if thelength of the cylindrical holes is such that equation (1) is satisfied.

In order for single surface-transformed spheres to combine with othersurface-transformed spheres, the center-to-center spacing (D_(NT))between the initial cylindrical holes will satisfy the followingequation:2×R _(C) <D _(NT)<3.76×R _(C).  (4)Satisfying this equation prevents the adjacent initial cylindrical holesfrom touching, yet allows the adjacent surface-transformed spheres tocombine and form pipe and plate empty spaces, as shown in FIGS. 5A-5Cand FIGS. 6A-6B and described below.

FIGS. 5A-5C illustrate a process to form a pipe-shaped empty space in agettering region, according to various embodiments of the presentinvention. A linear array of cylindrical holes 511 is formed through asurface 512 of a semiconductor volume where at least part of the volumeforms a gettering region 502. The cylindrical holes 511 have acenter-to-center spacing (D_(NT)) as calculated using equation (4). Thesemiconductor material 502 is heated (annealed) and undergoes thetransformation illustrated in FIGS. 5B through 5C. The result of thesurface transformation process is an empty pipe-shaped void 514 formedbelow the surface 512 of the semiconductor volume 502. The radius(R_(P)) of the pipe-shaped void 514 is provided by the followingequation: $\begin{matrix}{R_{P} = {\sqrt{\frac{8.86 \times R_{C}^{3}}{D_{NT}}}.}} & (5)\end{matrix}$

FIGS. 6A-6B illustrate a process to form a plate-shaped empty space in agettering region, according to various embodiments of the presentinvention. A two-dimensional array of cylindrical holes 611 is formed ina surface 612 of a semiconductor volume where at least part of thevolume forms a gettering region 602. The cylindrical holes 611 have acenter-to-center spacing (D_(NT)) as calculated using equation (4). Thematerial 602 is heated (annealed) and undergoes the transformationillustrated in FIG. 6B. The result of the surface transformation processis an empty plate-shaped void 615 formed below the surface 612 of thevolume of material 602. The thickness (T_(P)) of a plate 320 is given bythe following equation: $\begin{matrix}{T_{P} = \frac{27.83 \times R_{C}^{3}}{D_{NT}^{2}}} & (6)\end{matrix}$

The voids are formed in a gettering region using surface transformation.In various embodiments, a precisely-determined arrangement of voids isformed using surface transformation to provide a large interior voidsurface to volume ratio and to provide a desired distribution of thevoids throughout the gettering region. In various embodiments, the voidsin the gettering region include nano-sized voids (“nano-voids”). Invarious embodiments, the present subject matter forms aprecisely-determined arrangement of voids using surface transformationto provide a cellular material with a predictable mechanical failure fora given force. In various embodiments, the present subject matter formsa precisely-determined arrangement of voids using surface transformationto provide a cellular material with an anisotropic stiffness.

The size, shape and spacing of empty spaces is controlled by thediameter, depth and spacing of holes (or trenches) initially formed in asemiconductor material that has a defined melting temperature. Emptyspaces or voids are formed after annealing the material in a temperaturerange below and near the defined melting temperature. The empty spacesor voids are capable of being formed with a spherical shape, a pipeshape, plate shape, various combinations of these shape types, and/orvarious dimensions for the various shape type and combinations of shapetype. The volume of air incorporated in the surface transformed emptyspaces is equal to the volume of air within the initial starting patternof cylindrical holes. Thus, the surface transformed empty spaces do notcause additional stress in the material or a tendency for the materialto crack.

The surface of the semiconductor volume will be smooth after the surfacetransformed empty spaces are formed if the initial cylinder length (L)is equal to an integer of a critical length (λ_(c)) such as 1×λ_(c) toform one sphere, 2×λ_(c) to form two spheres, 3×λ_(c) to form threespheres, etc. If the cylinder length (L) is not equal to an integer of acritical length (λ_(c)), then the surface will have dimples caused byair in the cylinder attributable to the length beyond an integer of acritical length (λ_(c)). That is, for a given length L and λ_(c), thenumber of spheres formed is the integer of L/λ_(c), and the remainder ofL/λ_(c) contributes to the dimples on the surface.

FIGS. 7A-7E illustrate the formation of empty spheres in a getteringregion from initial cylindrical holes with the same radii and withvarying length, according to various embodiments of the presentinvention. Initial cylindrical holes are represented using dashed lines711. These initial cylindrical holes 711 have the same radius (R_(C))and are drilled or otherwise formed to different depths as representedby FIGS. 7A, 7B, 7C, 7D and 7E. The resulting surface-transformedspheres 713 are illustrated with a solid line, as are the surfacedimples 716 that form when the cylindrical hole depth is not an integermultiple of λ_(C). These surface dimples can be removed using a simplepolishing process to leave a smooth surface with uniform and closedspherical voids within the material. A crystalline semiconductor can beformed over the polished gettering region for use in fabricatingsemiconductor devices. The vertical position and number of the sphericalvoids is determined by the depth of the initial cylindrical holes.

In various embodiments of the present subject matter, the getteringregion of the semiconductor substrate is formed by appropriately spacingthe initially-formed holes such that, upon annealing the semiconductormaterial to provide the surface transformation process, the resultingvoids are uniformly spaced (or approximately uniformly spaced)throughout the gettering region. The uniformly spaced voids provide thegettering region with the ability to getter a device region with moreuniformity. Smaller voids provide more gettering uniformity. With morepredictable gettering of device regions, the performance of the devicesformed therein is more predictable, thus providing better yield.

In various embodiments, it is desirable to provide a gettering regionwith voids to provide a high internal void surface to volume ratio toimprove gettering. The interior void surfaces have dangling bonds thatare highly chemically reactive, and are useful to getter impurities.

FIG. 8 illustrates a transformation formed stack of empty plates 815 ina gettering region 802, according to various embodiments of the presentinvention. For example, the illustrated filling factor, f, isapproximately equal to 0.78, which provides a relatively high porosity,a relatively low density, and a relatively high internal void surface tovolume ratio. In the illustrated example, the surface transformationproduces a vertical stack of empty plates in the materials. The numberof empty plates formed depends on the length of the holes. Variousembodiments of the vertical stack includes one ore more empty plates.From equation (6), it is determined that the thickness T_(P) of theempty plate has a maximum value of 6.95×R_(C) when D_(NT) is near theminimum allowed value of 2×R_(C) as inferred from equation (4). Fromequation (3), the center-to-center spacing (λ) of empty plates is8.89×R_(C). It can be calculated that f≈0.78.

In various embodiments of the present subject matter, a plurality ofspace group symmetries of empty spheres of equal size are formed in asolid material.

FIG. 9 illustrates fourteen representative unit cells of space latticeswhich the voids in the gettering region can form, according to variousembodiments of the present invention. For simplicity, only the cubic Punit cell of FIG. 9 with a lattice constant “a₀” is discussed below. Oneof ordinary skill in the art will understand, upon reading andcomprehending this disclosure, how to form void patterns for the otherunit cells illustrated in FIG. 9. Each void in the unit cell can be thesame shape (e.g. sphere-shaped, plate-shaped or pipe-shaped voids). Invarious embodiments, the unit cell includes different combinations ofsphere-shaped, plate-shaped, or pipe-shaped voids.

FIG. 10 illustrates a void pattern in a gettering region arranged toform the cubic P unit cell shown among the fourteen representative unitcells of FIG. 9. A defined set of cylindrical holes are drilled orotherwise formed into the gettering region to form empty spheres 1013 ofthe same radius in the solid material at each of the illustrated unitcell lattice positions. For simplicity, the formation of one unit cellin the x-y plane and n unit cells in the z direction is discussed.Additional unit cells in the x-y planes are formed by repeatedlytranslating the hole pattern for the unit cell in the x and ydirections. From equations (2) and (3), spheres are created withperiodicity a₀ in the Z direction by drilling or otherwise forming theholes in the Z direction such that the radius of the holes (R_(C)) arerepresented by the following equation: $\begin{matrix}{R_{C} = {\frac{a_{0}}{8.89} \approx {0.11 \times {a_{0}.}}}} & (7)\end{matrix}$After surface transformation, the radius, R_(S) of each formed emptysphere is: $\begin{matrix}{R_{S} = {{\frac{1.88}{8.89} \times a_{0}} \approx {0.212 \times {a_{0}.}}}} & (8)\end{matrix}$In order to form n unit cells in the Z direction through surfacetransformation, the depth (L_(n)) of the initial cylinder in the Zdirection is:L _(n)=(n+1)×a ₀=(n+1)×8.99×R _(C).  (9)To form a single cubic P unit cell in the Z direction, n is set to 1 forthe two deep arrangement of spheres such that the cylindrical holes areformed to the following hole depth:L ₁=2×8.89×R _(C)=2×a ₀.  (10)

FIGS. 11A-11B illustrate a process for forming a cubic P lattice ofspherical empty spaces, according to various embodiments of the presentinvention. Referring to FIG. 11A, four cylindrical holes 1111A, 1111B,1111C and 1111D of radius Rc=0.11×a₀ are formed into the semiconductorvolume 1102 from a surface 1112 to a depth L=2×a₀. The four cylindricalholes 1111A, 1111B, 1111C and 1111D are spaced apart along the x and yaxes at a distance a₀. The solid material is annealed near its meltingtemperature to form sphere-shaped empty spaces 1113A, 1113B, 1113C,1113D, 1113E, 1113F, 1113G and 1113H by surface transformation atdesired sites of the cubic P unit cell as is shown in FIG. 11B.

One of ordinary skill in the art will understand, upon reading andcomprehending this disclosure, that the unit cells of each primitivelattice in FIG. 6 can be formed to have equal sized empty spheres ateach lattice site by forming in the Z direction an appropriate patternof cylindrical holes of the same diameter in the x-y plane. Theprescribed depths for these unit cells will generally be different.

In various embodiments, space lattices having more than one size ofempty spheres in the unit cell are formed by forming initial cylindricalholes of more than one radius. In various embodiments, the holes areformed in more than one direction. The number of surface transformationannealing steps used to form the space lattice depends on the structureto be formed. A method to form a simple illustrative structural unit ofempty spheres is described below.

FIGS. 12A-12D illustrate a process for forming a simple unit of emptyspheres having two radii in a gettering region, according to variousembodiments of the present invention. The desired structure has fourempty spheres of radius R_(S)=0.212×a₀, and four empty spheres of radiusR_(S′)=½×R_(S)=0.106×a₀. All of the empty spheres have a closestcenter-to-center spacing of a₀/2. The process to form theabove-described structure is illustrated in FIGS. 12A, 12B, 12C and 12D.

In FIG. 12A, two cylindrical holes 1211A of radius, R_(C)=0.11×a₀ and oflength L=2×a₀ are formed in the Z direction. The solid material isannealed to effect surface transformation and form the four spheres1213A with R_(S)=0.212×a₀, as shown in FIG. 12B.

In FIG. 12C, two cylindrical holes 1211B are drilled in the y-direction.These holes 1211B have a radius R_(C′)=0.055a₀, and a length L′=a₀.Again the material is annealed to effect surface transformation and thefour smaller empty spheres 1213B to form the desired structure shown inFIG. 12D. The second annealing step only effects the cylindrical holessince they are not energetically stable. The four previously formedlarger empty spheres are stable since they were formed during the firstannealing.

Another method for forming the structure in FIG. 12D involves formingthe cellular material in various deposition layers and forming the voidsusing a surface transformation process (i.e. hole formation andannealing) for each layer before a successive layer of material isdeposited. Using this method, the structure illustrated in FIG. 12D isformed by a first deposition process, a first surface transformationprocess, a second deposition process, a second surface transformationprocess, a third deposition process, a third surface transformationprocess, a fourth deposition process, and a fourth surfacetransformation process. Each surface transformation step includes holeformation and annealing. For each layer, the hole formation pattern iscalculated to achieve the desired spacing of resulting voids, bothbetween and within layers, after the layer is annealed.

One of ordinary skill in the art will understand, upon reading andcomprehending this disclosure, that a number of void arrangements arecapable of being formed, a number of void sizes are capable of beingformed, and that various combinations of void arrangements and voidsizes are capable of being formed. One of ordinary skill in the art willunderstand, upon reading and comprehending this disclosure, that variousdifferent shapes of empty spaces can be formed, and that these variousdifferent shapes of empty spaces can be combined with other shapes ofempty spaces. For example, a cellular material can include a number ofsphere-shaped voids, a number of pipe-shaped voids, a number ofplate-shaped voids, and various combinations of sphere-shaped void(s),pipe-shaped void(s), and plate-shaped void(s). One of ordinary skill inthe art will understand, upon reading and comprehending this disclosure,that the various shapes can be stacked, and that various differentshapes can be stacked together. For example, an arrangement of spherescan be stacked on top of an arrangement of plates. Additionally, eachstack of voids can include various shapes. The precisely-determinedarrangement of empty spaces is determined by the position, depth anddiameter of the holes formed prior to the annealing process.

The figures presented and described above are useful to illustratemethod aspects of the present subject matter. Some of these methodaspects are described below. The methods described below arenonexclusive as other methods may be understood from the specificationand the figures described above.

FIG. 13 illustrates a process for forming semiconductor devices,according to various embodiments of the present invention. At 1320,voids are precisely formed and are located to getter a device region. At1321, subsequent semiconductor fabrication processes are performed, Asrepresented at 1322, these subsequent semiconductor fabricationprocesses include forming a semiconductor device in a device region. Anexample of a semiconductor device is a transistor. In variousembodiments, these semiconductor processes include depositing asemiconductor such as crystalline silicon on the gettering region, andforming a transistor using the crystalline silicon. In variousembodiments, the voids are formed in a crystalline semiconductor volume,and the devices are formed using the crystalline semiconductor above thevoids. In various embodiments, the voids are formed in a crystallinesemiconductor volume, and the devices are formed using the crystallinesemiconductor adjacent to the voids.

FIG. 14 illustrates a process for precisely forming voids in a substratelocated to getter a device region as performed in the process forforming semiconductor devices of FIG. 13. The illustrated process 1420generally corresponds to the 1320 in FIG. 13. In the illustratedembodiment, holes are formed to extend from a substrate surface and intoa semiconductor substrate at 1423. The holes have a predetermined sizeand shape, and are formed in a predetermined location or pattern oflocations in the substrate. In various embodiments, the holes have agenerally cylindrical shape. At 1424, the substrate is annealed to formpredetermined voids in the substrate. The substrate has a well-definedmelting temperature, and the annealing temperature is slightly below themelting temperature. Depending on the size, shape and pattern of holesformed at 1423, the voids can include sphere-shape voids, a pipe-shapevoids and/or plate-shaped voids.

The present subject matter provides the ability to form getteringregions with a precisely-determined arrangement of precisely-formedvoids using surface transformation. In various embodiments, theprecisely-determined arrangement of precisely-formed voids includeuniformly spaced and closed voids that provide the gettering region withuniform gettering characteristics and with a large internal surface tovolume ratio to provide a large number of uniformly distributed danglingbonds (defects in the crystalline structure) in proximity to a deviceregion to effectively getter the device region. Thus, by effectivelyremoving impurities from device regions, semiconductor devices are cableof being precisely fabricated.

System Level

FIG. 15 is a simplified block diagram of a high-level organization of amemory device, according to various embodiments of the presentinvention. The illustrated memory device 1530 includes a memory array1531 and read/write control circuitry 1532 to perform operations on thememory array via communication line(s) 1533. The illustrated memorydevice 1530 may be a memory card or a memory module such as a singleinline memory module (SIMM) and dual inline memory module (DIMM). One ofordinary skill in the art will understand, upon reading andcomprehending this disclosure, that semiconductor components in thememory array 1531 and/or the control circuitry 1532 are able to befabricated using the gettering regions having precise patterns of voidsformed by surface transformation, as described above.

The memory array 1531 includes a number of memory cells 1534. The memorycells in the array are arranged in rows and columns. In variousembodiments, word lines 1535 connect the memory cells in the rows, andbit lines 1536 connect the memory cells in the columns. The read/writecontrol circuitry 1532 includes word line select circuitry 1537, whichfunctions to select a desired row. The read/write control circuitry 1532further includes bit line select circuitry 1538, which functions toselect a desired column.

FIG. 16 is a simplified block diagram of a high-level organization of anelectronic system, according to various embodiments of the presentinvention. In various embodiments, the system 1640 is a computer system,a process control system or other system that employs a processor andassociated memory. The electronic system 1640 has functional elements,including a processor or arithmetic/logic unit (ALU) 1641, a controlunit 1642, a memory device unit 1643 (such as illustrated at 1530 inFIG. 15) and an input/output (I/O) device 1644. Generally such anelectronic system 1640 will have a native set of instructions thatspecify operations to be performed on data by the processor 1641 andother interactions between the processor 1641, the memory device unit1643 and the I/O devices 1644. The control unit 1642 coordinates alloperations of the processor 1641, the memory device 1643 and the I/Odevices 1644 by continuously cycling through a set of operations thatcause instructions to be fetched from the memory device 1643 andexecuted. According to various embodiments, the memory device 1643includes, but is not limited to, random access memory (RAM) devices,read-only memory (ROM) devices, and peripheral devices such as a floppydisk drive and a compact disk CD-ROM drive. As one of ordinary skill inthe art will understand, upon reading and comprehending this disclosure,any of the illustrated electrical components are capable of beingfabricated to include the silicon germanium proximity gettering regionin accordance with various embodiments of the present invention.

The illustration of the system 1640 is intended to provide a generalunderstanding of one application for the structure and circuitry, and isnot intended to serve as a complete description of all the elements andfeatures of an electronic system using proximity gettering regionsaccording to the various embodiments of the present invention. As one ofordinary skill in the art will understand, such an electronic system canbe fabricated in single-package processing units, or even on a singlesemiconductor chip, in order to reduce the communication time betweenthe processor and the memory device.

Applications containing a gettering region as described in thisdisclosure include electronic systems for use in memory modules, devicedrivers, power modules, communication modems, processor modules, andapplication-specific modules, and may include multilayer, multichipmodules. Such circuitry can further be a subcomponent of a variety ofelectronic systems.

Various embodiments disclosed herein getter a semiconductor wafer byprecisely forming voids, such as nano-voids, at desired locations in thewafers. Various embodiments form an even distribution of voids acrossthe wafer below device regions. In various embodiments, precisely-formedgettering void patterns are formed proximate to selected regions wheredevices are fabricated on the semiconductor wafer. Various embodimentsprecisely form the void patterns below device regions. Numerous danglingbonds are present at the internal surfaces of the voids such that theseinternal surfaces are highly chemically reactive. Thus, variousembodiments form the voids and void patterns to have the greatestsurface to volume ratio to increase the gettering of impurities.

This disclosure includes several processes, circuit diagrams, andstructures. The present invention is not limited to a particular processorder or logical arrangement. Although specific embodiments have beenillustrated and described herein, it will be appreciated by those ofordinary skill in the art that any arrangement which is calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This application is intended to cover adaptations or variations.It is to be understood that the above description is intended to beillustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments, will be apparent to those of skillin the art upon reviewing the above description. The scope of thepresent invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

1. A memory device, comprising: at least one gettering region formed ina semiconductor substrate, the gettering region including a precisearrangement of precisely-formed voids to getter impurities from acrystalline semiconductor region of the substrate; a memory array formedin the crystalline semiconductor region, including a plurality of memorycells formed in rows and columns, and at least one transistor for eachof the plurality of memory cells; a plurality of word lines, each wordline being connected to a row of memory cells; a plurality of bit lines,each bit line being connected to a column of memory cells; and controlcircuitry, including word line select circuitry and bit line selectcircuitry to select a number of memory cells for writing and readingoperations.
 2. The device of claim 1, wherein the precise arrangement ofthe plurality of voids is uniformly distributed through the getteringregion.
 3. The device of claim 1, wherein the plurality of voids areseparated by a critical length (λ_(C)) that is dependent on a radius(R_(C)) of a number of holes used to form the plurality of voids using asurface transformation process.
 4. The device of claim 1, wherein eachof the voids has an interior surface that includes dangling bonds suchthat the plurality of voids getter impurities from the at least onedevice region.
 5. The device of claim 1, wherein: the at least onegettering region has a volume; and the precisely-determined arrangementof the plurality of precisely-formed voids is formed to provide a largeratio between the interior surface of the plurality of precisely-formedvoids and the volume to enhance gettering of the crystallinesemiconductor region.
 6. The device of claim 1, wherein the plurality ofprecisely-formed voids includes a sphere-shaped void.
 7. The device ofclaim 1, wherein the plurality of precisely-formed voids includes apipe-shaped void.
 8. The device of claim 1, wherein the plurality ofprecisely-formed voids includes a plate-shaped void.
 9. A memory device,comprising: at least one gettering region formed in a semiconductorsubstrate, the gettering region including a precise arrangement ofprecisely-formed voids to getter impurities from a crystallinesemiconductor region of the substrate, wherein the plurality of voidsare separated by a critical length (λ_(C)) that is dependent on a radius(R_(C)) of a number of holes used to form the plurality of voids using asurface transformation process, and the plurality of precisely-formedvoids includes a sphere-shaped void; a memory array formed in thecrystalline semiconductor region, including a plurality of memory cellsformed in rows and columns, and at least one transistor for each of theplurality of memory cells; a plurality of word lines, each word linebeing connected to a row of memory cells; a plurality of bit lines, eachbit line being connected to a column of memory cells; and controlcircuitry, including word line select circuitry and bit line selectcircuitry to select a number of memory cells for writing and readingoperations.
 10. The device of claim 9, wherein each of the voids has aninterior surface that includes dangling bonds such that the plurality ofvoids getter impurities from the at least one device region.
 11. Thedevice of claim 9, wherein: the at least one gettering region has avolume; and the precisely-determined arrangement of the plurality ofprecisely-formed voids is formed to provide a large ratio between theinterior surface of the plurality of precisely-formed voids and thevolume to enhance gettering of the crystalline semiconductor region. 12.The device of claim 9, wherein the precise arrangement of the pluralityof voids is uniformly distributed through the gettering region.
 13. Amemory device, comprising: at least one gettering region formed in asemiconductor substrate, the gettering region including a precisearrangement of precisely-formed voids to getter impurities from acrystalline semiconductor region of the substrate, wherein the pluralityof voids are separated by a critical length (λ_(C)) that is dependent ona radius (R_(C)) of a number of holes used to form the plurality ofvoids using a surface transformation process, and the plurality ofprecisely-formed voids includes a pipe-shaped void; a memory arrayformed in the crystalline semiconductor region, including a plurality ofmemory cells formed in rows and columns, and at least one transistor foreach of the plurality of memory cells; a plurality of word lines, eachword line being connected to a row of memory cells; a plurality of bitlines, each bit line being connected to a column of memory cells; andcontrol circuitry, including word line select circuitry and bit lineselect circuitry to select a number of memory cells for writing andreading operations.
 14. The device of claim 13, wherein each of thevoids has an interior surface that includes dangling bonds such that theplurality of voids getter impurities from the at least one deviceregion.
 15. The device of claim 13, wherein: the at least one getteringregion has a volume; and the precisely-determined arrangement of theplurality of precisely-formed voids is formed to provide a large ratiobetween the interior surface of the plurality of precisely-formed voidsand the volume to enhance gettering of the crystalline semiconductorregion.
 16. The device of claim 13, wherein the precise arrangement ofthe plurality of voids is uniformly distributed through the getteringregion.
 17. A memory device, comprising: at least one gettering regionformed in a semiconductor substrate, the gettering region including aprecise arrangement of precisely-formed voids to getter impurities froma crystalline semiconductor region of the substrate, wherein theplurality of voids are separated by a critical length (λ_(C)) that isdependent on a radius (R_(C)) of a number of holes used to form theplurality of voids using a surface transformation process, and theplurality of precisely-formed voids includes a plate-shaped void; amemory array formed in the crystalline semiconductor region, including aplurality of memory cells formed in rows and columns, and at least onetransistor for each of the plurality of memory cells; a plurality ofword lines, each word line being connected to a row of memory cells; aplurality of bit lines, each bit line being connected to a column ofmemory cells; and control circuitry, including word line selectcircuitry and bit line select circuitry to select a number of memorycells for writing and reading operations.
 18. The device of claim 17,wherein each of the voids has an interior surface that includes danglingbonds such that the plurality of voids getter impurities from the atleast one device region.
 19. The device of claim 17, wherein: the atleast one gettering region has a volume; and the precisely-determinedarrangement of the plurality of precisely-formed voids is formed toprovide a large ratio between the interior surface of the plurality ofprecisely-formed voids and the volume to enhance gettering of thecrystalline semiconductor region.
 20. The device of claim 17, whereinthe precise arrangement of the plurality of voids is uniformlydistributed through the gettering region.